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Abandoned Mine Initiative

Townsend's big-eared bat (Corynorhinus townsendi) is one of nine bat species that use the Montana mine in Ruby, AZ. Photo: Brian Corbett

Peppered across the entire continent, the estimated 500,000 abandoned mines throughout the United States present many potent dangers to human health and the environment. In recent years, state and federal government agencies have been ramping up reclamation and closure of these potential hazards.

The vast majority of these lands no longer serve their original function as a source of ore or minerals. Often in very remote places, removed from disturbance and in the midst of abundant other natural resources, some of these abandoned mines have become important habitat for bats as they seek refuge from encroachment by human development or other intrusions elsewhere. The Montana mine in the ghost town of Ruby, Arizona, for example, is used by nine species of bats year round.

Yet many government and private entities lack the resources necessary to effectively address or confirm the presence of bats in mines. This results in closure plans that may jeopardize bat species by destroying the habitat, or worse, inadvertently entombing a colony inside.

BCI’s SubT team works closely with federal, state and private land managers to identify and evaluate potential bat roosting sites. On average, team members spend two weeks of each month in the field working with agencies including the Bureau of Land Management, Department of Defense, Forest Service, and state mining and minerals offices, conducting biological surveys and mapping underground areas.

Evidence of bat presence identified through SubT assessments—including ceiling stains, guano, insect remains and roosting bats themselves—enables partners to pursue viable management plans for each site. One of the most effective strategies for preserving quality bat habitat is the installation of steel bat gates and cupolas, which allows bats access to the mine, keeps people out, and eliminates the need to seal off or destroy the mine itself.

Since its inception in 2008, the SubT team has surveyed over 5,000 mine features and 400 natural caves as part of its Abandoned Mine Initiative. Of these, BCI has recommended or assisted with the installation of bat compatible closure at nearly a thousand abandoned mines, ensuring their availability for bats for many years to come.

Of the 47 bat species in North America, 18 rely heavily on caves during the year, including 13 species that live in subterranean habitat year-round. Five species depend on caves and underground habitat for hibernation.

But not all caves, cliff crevices, abandoned mines or underground spaces provide adequate habitat for bats; in fact, most do not, due to unsuitable temperature and humidity levels, exposure to light, disturbance by humans and predators, and distance from food and water resources. That means that there are relatively few subterranean spaces that many species of bats rely on, so identifying these places and protecting them are critical for their continued survival.

Who’s Living in Caves?

In the eyes of bats, not all caves are equal. And the reasons they use the underground differ depending on the species and time of year.

Caves and mines can serve as daytime roosts, where bats like the western small-footed myotis (Myotis ciliolabrum) sleeps during daylight hours; or as night roosts, where some species will head to rest and digest between nighttime foraging sessions, such as Townsend’s big-eared bat (Corynorhinus townsendii).

Bats seek out subterranean habitat for hibernation, sometimes individually, and sometimes in huge groups, like the little brown bat (Myotis lucifugus), which can congregate in the hundreds of thousands for winter hibernation. These hibernacula can also host mixed groups of different bat species, like the northern long-eared bat (Myotis septentrionalis). Unfortunately, this also enables easier transmission of the fungal pathogen that causes White-nose Syndrome, a deadly disease that has been wiping out little browns in the East and has been documented on at least six other species of cave-reliant bats.

In the summer, caves also often serve as sites for maternity roosts. The 20 million Mexican free-tailed (Tadarida brasiliensis) bats roosting in Texas’s Bracken Cave from March through October go there for a safe, warm environment in which to birth their pups. Over 500 pups per square foot have been observed crowding parts of the cave’s ceiling, huddling together for warmth and protection.

The endangered gray bat (Myotis grisescens) of the southeastern U.S. relies on caves for hibernating, breeding and summer roosting. This species uses them as dispersal and stopover sites during migration.

Underground spaces are also known to be important places for social and mating interactions between males and females, or juveniles and adults. Indiana bats (Myotis sodalis) will swarm, or fly in and out of cave entrances throughout the night without roosting there, a behavior linked with mating encounters. It may also serve as a way for young bats to learn the location of hibernation sites.

Even some tree-roosting bats, like Utah’s western red bat (Lasiurus blossevillii) have been found roosting in caves and mines on occasion and silver haired bats (Lasionycteris noctivagans) have been observed, by BCI's SubT team, hibernating in abandoned uranium mines in both Colorado and Utah.

Work in the West

Big skies and (sometimes) even bigger terrain, a large part of the SubT's team's work takes place in the western United States. Photo: Katie Jepson / Bat Conservation International

The BCI Subterranean Program team’s members have been all over the United States, and even different parts of the world, to share their expertise and knowledge for preserving the subterranean world for bats.

A large part of the SubT team’s work takes place in the western half of the United States, where the majority of the country’s abandoned mines are located. Here, the SubT team works side-by-side with local, state and federal partners to evaluate whether a given abandoned mine area is used by bats, and how best to manage the closure of that land to mitigate human health impacts.

But that’s not all the Sub-T team does in the West.

White-nose Syndrome Monitoring

After the fungal pathogen that causes white-nose syndrome in bats was detected in Washington State in 2016, the SubT team and BCI biologists assisted state agencies with additional surveys to look for more evidence of the disease in Washington, Oregon and Idaho. The work also resulted in characterization of 20 new habitats over a three-month period, followed up by a series of re-surveys later that year.

But, as early as 2010, BCI's SubT Program was working with state and federal partners to survey and characterize winter roosts across the southwest and to collect substrate samples for the then, in-vogue, WNS detection method.

Bat Monitoring Protocol

A member of the SubT team collects a guano sample.Photo: Shawn Thomas / Bat Conservation International

As part of the large-scale, collaborative effort to establish the North American Bat Monitoring Protocol, BCI’s SubT team has been working with the Department of Defense to install and maintain acoustic devices at the White Sands Missile Range, where some of the monitoring is taking place. The initiative seeks to monitor bat populations across the country and monitor for early warning signs of population declines. Data will be gathered from a variety of sources, including hibernaculum counts in caves and mines, counts in summer maternity colonies, mobile acoustic surveys along roads, and from stationary acoustic equipment.

National Parks Bat Use Studies

In Death Valley National Park, the SubT team is conducting mapping and bat species inventories in the early-1900s Skidoo gold mine. Along with a physical map of the historic archaeological site, the surveys will help the National Park Service locate important bat areas within the mine, including identification of the primary exits bats use to come and go and to help with further management of the site.

Other Wildlife Surveys

While monitoring for bats in mines and other subterranean structures, the SubT team also gathers data on the other types of wildlife they encounter in these places, including Desert Tortoises, Barn Owls, Rock-skinned Newts, Ptarmigans, porcupines, foxes and even coati. These data are valuable not only to land managers concerned with usage of the site, but also in a broad scientific sense, as the data contribute to reference resources including species distribution maps, habitat types and population counts.

Endangered Species Success Story

Lesser Long-Nosed Bat (Leptonycteris yerbabuenae)

The lesser long-nosed bat Leptonycteris yerbabuenae is one of the primary pollinators of the agave plant. Photo: Bruce D. Taubert

Listed as a federally endangered species in 1988, this nectar-feeding resident of the desert Southwest was proposed for removal from the Endangered Species list. The BCI SubT team was instrumental in conducting exhaustive searches for unknown roosts, as well as careful surveys of known roosts, of the lesser long-nosed bat throughout its range in the United States.

When initially listed, there were believed to be fewer than 1,000 bats at 14 known roosts. Today, there are an estimated 200,000 bats at 75 roosts, and the lesser long-nosed is awaiting final approval for ESA delisting

Already engaged in surveys in the region, the SubT program leveraged additional funding from NRCS and SWIG grants to survey every possible mine they could locate in southern Arizona. The team located target sites through a combination of discussions with local residents, scouring historic records and documents, and looking for signs of subterranean entrances on satellite and aerial maps, the team believes it has, along with other partners survey efforts, accounted for nearly every possible underground roosting site that lesser long-nosed bats might take advantage of.

This information enabled the U.S. Fish and Wildlife Service to better understand the stability of bat populations at extant roosts, as well as overall availability of habitat, two key factors in a process that ultimately led the agency to recommend the species for delisting.

The Underground

Cool, dark, peaceful and calm, the subterranean world is a many a bat’s perfect escape from the din and clatter of the daytime. Whether alone or in massive colonies, bats are uniquely suited to take advantage of the many benefits caves confer. For hibernating, resting during the day, at night between meals, for mating, or for social meet-ups, underground spaces in their myriad forms are important places for many species of North American bats.

Roughly half of all of North American bat species rely on subterranean habitat for at least some part of their life cycle. Though not all bats live in caves, and not all caves have bats, they hold outsized importance for the chiropterans that do rely on them. Because many individuals tend to congregate in relatively few roosting sites during breeding or hibernation, disturbance of even one site can impact a large proportion of a given species.

Do cave bats only live in caves?

No! Although some bats have evolved to live in caves, they can, and do, take advantage of any cave-like structure with the right environmental conditions. This include the obvious, like sinkholes and abandoned mines, but also places people don’t tend to think of as often: bunkers, burial crypts, basements, derelict sewer systems, and crevices in cliffs. Some bats will only hibernate in these structures, while others migrate and occupy them seasonally.

A pair of Townsend's big-eared bats are flying in an abandoned mercury sulfide mine in central Oregon.Photo: Michael Durham/Minden Pictures

Why did bats go underground in the first place?

Science is still working out exactly why bats headed under the hills at some point during their evolution. One reason may be due to their wings: all that exposed skin makes them susceptible to dehydration, and caves provide habitat with relatively high humidity. They’re also safer from predators.

Caves also provide stable habitat for very long stretches of time, even as climate conditions above may be changing. Access to a variety of underground roosting spaces is key for bats to able to exploit shifting conditions, or to expand into new areas.

Does every cave or mine have bats living in it?

No. In fact, only a small fraction of available subterranean habitat is suitable for the bats that need it. In temperate North America, many underground features are simply too cold for bats to occupy them long-term; they must have the right kind of airflow, humidity levels, ceiling texture and light levels for bats to choose to settle down there. But when a site does check all the right boxes, it’s one bats will return to again and again.

How do we know which subterranean places are most important to bats?

Through careful, systematic and sustained observation and investigation of sites suspected or reported to be frequented by bats. BCI’s SubT program team is equipped with a specialized set of skills to be able to venture into these hard-to-reach places and confirm which sites are used by bats, as well as gather biological and environmental data about the bats and their roosting sites.

The team also uses this data to advise land management partners in the public and private sectors regarding proper closure of mines and other potentially hazardous subterranean features; for instance, helping coordinate installation of gates at known bat habitats to keep people out while still allowing bats access to a roosting or hibernation site.

What are the greatest threats to these kinds of habitats?

In general, human disturbance poses the greatest threats to natural and manmade bat habitat. While cave exploration is a popular pastime for many people, careless visitors can prompt bats can abandon a roost after even short periods of disturbance. Humans can also inadvertently carry in pathogens on their clothes or shoes that can be harmful to the bats living there. And in expanding urban and suburban areas, development around caves or old mine reduces or eliminates foraging habitat and puts humans in closer proximity to the roosts.

Permanent Habitat Protection

Besides the placement of bat compatible closures and mines and caves, the SubT Program also actively works toward to permanent protection of important bat roosts on private lands by donation or purchase. While BCI is not in the business of land ownership, we work closely with several organizations that hold such sites and manage them for the long term success of the bats that call them home. Please contact us if you know of a privately owned site that needs protection or if you would like to donate a property.

Subterranean Work

Roughly half of all bat species in North America rely on subterranean habitat for some part of their life cycle. In caves, mines, basements and even abandoned sewers, bats find shelter from predators and the elements. Here, they can safely sleep, hibernate, mate, raise young and rest during long migrations.

Because the underground environment plays so central a role for so many kinds of bats, a better understanding of these hidden landscapes is crucial for creating and advancing successful conservation strategies.

Launched in 2008, BCI’s Subterranean Program works to increase the overall knowledge of underground environments and the bats that use them and to permanently protect them. The SubT team accomplishes this through a wide range of environmental assessments in caves, mines, and other subterranean structures.

These assessments include identifying suitable habitat, documenting evidence of use by bat species, and characterizing the overall underground environments where bats seek refuge.

Unfortunately, some of the same environments where bats flourish can be hazardous for humans, especially abandoned mines, and are often targeted for closure or destruction. The SubT team helps bridge the gap between preserving these vital habitats while also safeguarding the public from potential subterranean hazards.

The Team

The SubT team consists of a talented group of biologists that include Program Director Jason Corbett, Program Manager Shawn Thomas, Field Lead Nathan Breece, and numerous other part-time experts stationed around the country.

Their passion for bats is matched by their penchant for exploring the unknown: rappelling underground, crawling though mine passages, and mapping uncharted cave corridors. All the while, the team is on the look out for evidence of bat activity, such as discarded insect parts on cave or mine floors, roost stains on the ceiling, and of course, the bats themselves.

With their unique blend of scientific expertise and specialized training in navigating the dangerous underground, the team ensures land managers are taking bats and their needs into account whenever potential habitat is targeted for closure. This takes a variety of forms: advising and facilitating on installation of bat gates, targeted bats and mines training, public education, research, and sharing of collected documentation and data.